Suspensions for high clearance agricultural vehicles such as the John Deere 4720 Sprayer utilize a linkage to translate torque from a steering cylinder input to the suspension spindle. Such a linkage is shown, for example, in commonly assigned U.S. Pat. No. 5,597,172 and includes a pneumatic spring supported above a strut shaft which is received within a strut journal connected to an adjustable axle. A scissors assembly located above the axle maintains wheel steer while facilitating vertical movement of the strut shaft within the journal. On non-steerable wheels, the lower end of the scissors assembly is connected to the journal to maintain a preselected wheel orientation. For steerable wheels, the lower end of the scissors assembly is connected to a hydraulic steering structure which allows axle adjustments for varying wheel tread. Although the scissors structure functions well to keep the steering cylinder in plane during vertical motion of the strut shaft, such an assembly is relatively expensive and requires maintenance.
Another type of suspension system includes a steering cylinder attached at one end to the chassis and at the other end to the suspension. Although such a system can be simpler and less costly than the scissors assembly, the effective cylinder length will change with suspension travel causing undesirable changes in the steering angle and steering control problems. In systems wherein: the cylinder mounted to move vertically with the suspension, other problems can arise such as bracket complexity and cost, cylinder clearance and cylinder hose routing requirements, and added potential for cylinder and cylinder hose damage.